Corrosion resistant sintered stock containing mixed carbides



United States Patent CORROSION RESISTANT SINTERED STOCK CONTAINING MIXEDCARBIDES John C. Redmond, Greensburg, and John W. Graham, Ligonier, Pa.,assignors to Kenname'tal Inc., Latrobe, Pa., a corporation ofPennsylvania No Drawing. Application October 8, 1952, Serial No. 313,810

3 Claims. (Cl. 29-182.7)

Our invention relates to an improved corrosion-resistant hardcomposition of matter and has to do, more particularly, withimprovements in the corrosion-resistant hard composition of matterdescribed and claimed in the pending application for United StatesLetters Patent of Philip M. McKenna, Alex G. McKenna and John C.Redmond, Serial No. 268,004, filed January 24, 1952, as acontinuation-in-part of an earlier application, Serial No. 74,742,

filed February 5, 1949, now abandoned.

The principal object of our invention is to provide a sintered hardcomposition of matter which, with the density, hardness and resistanceto oxidation of the composition of said application, will have a greatertransverse rupture strength at room temperature.

A primary method of evaluation of compositions, such as those disclosedin said application, has been evolved and is called the stress-rupturetest. It consists of maintaining a static tensile load on a suitablespecimen at some specified elevated temperature until the specimen failsby breaking in tension in some interval of time between one and 1000hours. By testing a series of specimens at various loads and at onetemperature a graph can be drawn with time the abscissa and stress asthe ordinate. When scaled properly a straight line results. The testsare generally made at several temperatures to develop a range ofstress-temperature conditions. Various alloys or compositions arecompared by comparing the slopes of the lines on the several graphs. Afurther object of our invention is to provide a sintered hardcomposition of matter which gives better results under thestress-rupture test.

A further object of our invention is to provide a sintered'hardcomposition of matter having increased tensile strength and an increasedmodulus of elasticity.

Further objects, and objects relating to details and economies ofoperation, will appear more definitely from the detailed description tofollow.

In general, our invention consists in substituting, for

constitute from 20% to 50% of the composition, and the molybdenum shouldconstitute from 5% to 25% of the said alloy,

The following are specific examples of compositions made in accordancewith our invention.

Example I This composition consists of titanium carbide (TiC), a complexcarbide solid solution containing columbium,

tantalum, titanium and carbon and referred to herein as Cb(TaTi)C,nickel and molybdenum, in the following proportions, by weight:

2,711,009 Patented June 21, 1955 The titanium carbide used, in this andthe following examples, was substantially devoid of free titanium, freecarbon, oxides and nitrides, and prepared by the method described andclaimed in United States Letters Patent of Philip M. McKenna, No.2,515,463, patented Iuly'18, 1950. The Cb(TaTi)C used in this end andthe following examples contained about 45% columbium carbide (CbC),about 42.5% tantalum carbide (TaC) and about 12.5% titanium carbide(TiC) and was made in accordance with United States Letters Patent ofPhilip M. McKenna, No. 2,124,509, patented July 19, 1938. The proportionof the ingredients of Cb(TaTi)C, given above, are not critical and mayvary somewhat depending on the columbite ore used to make it.

The hard composition of matter made from the mix above specified, by theprocedure hereafter described, had a density of 6.06 grams per cubiccentimeter, a hardness of 88.7 on the Rockwell A scale, and a transverserupture strength at room temperature of 191,000 p. s. i. (pounds persquare inch). Tests of a number of specimens of this composition showedan average tensile strength of 119,300 p. s. i. (pounds per square inch)and an average Youngs modulus of elasticity between zero and maximumstress of 57.6 10 p. s. i. These values were considerably higher thanthose for a composition that was identical except that it contained nomolybdenum and 30% nickel. Specimens of the composition of Example Igave better results under the stress-rupture tests referred to above.This composition proved to be extremely resistant to corrosion oroxidation at high temperatures.

Example II This composition consists of titanium carbide (TiC), acomplex carbide solid solution containing columbium, tantalum, titaniumand carbon and referred to herein as Cb(TaTi)C, nickel and molybdenum,in the following proportions, by weight:

Per cent .TiC 57.0 Cb(TaTi)C 8.0 Ni 30.0 Mo 5.0

Example 111 This composition consists of titanium carbide (TiC),acomplex carbide solid solution containing columbium, tantalum, titaniumand carbon and referred to herein as Cb(TaTi)C, nickel and molybdenum,in the following proportions, by weight:

Per cent TiC 62.0 Cb(TaTi)C 8.0 Ni 28.5 Mo 1.5

The hard composition of matter made from the mix above specified, by theprocedure hereinafter described, had a density of 6.05 grams per cubiccentimeter, a hardness of 86.9 on the Rockwell A scale, and a transverserupture strength at room temperature of 155,000 p. s. i.

This composition proved to be extremely resistant to corrosion oroxidation at high temperatures.

Example IV This composition consists of titanium carbide (TiC), acomplex carbide solid solution containing columbium, tantalum, titaniumand carbon and referred to herein as Cb(TaTi)C, nickel and molybdenum,in the following proportions, by weight:

Per cent TiC 62.0 Cb(TaTi)C 8.0 Ni 22.5 Mo 7.5

The hard composition of matter made from the mix above specified, by theprocedure hereinafter described, had a density of 6.02 grams per cubiccentimeter, a hardness of 90.0 on the Rockwell A scale, and a transverserupture strength at room temperature of 173,750 p. s. i. Specimens ofthis composition gave improved results under the stress-rupture testsabove mentioned and this composition proved to be extremely resistant tocorrosion or oxidation at high temperatures.

Example V This composition consists of titanium carbide (TiC), a complexcarbide solid solution containing columbium, tantalum, titanium andcarbon and referred to herein as Cb(TaTi)C, nickel and molybdenum, inthe following proportions, by weight:

Per cent TiC 72.0 Cb(TaTi)C 8.0 Ni 16.7 Mo 3.3

Example VI This composition consisted of titanium carbide (TiC), acomplex carbide solid solution containing columbium, tantalum, titaniumand carbon and referred to herein as Cb(TaTi)C, nickel and molybdenum,in the following proportions, by weight:

Per cent TiC 72.0 Cb(TaTi)C 8.0 Ni 15.0 Mo 5.0

The hard composition of matter made from the mix above specified, by theprocedure hereinafter described,

and a density of 5.75 grams per cubic centimeter, a hardness of 91.8 onthe Rockwell A scale, and a transverse rupture strength at roomtemperature of 152,800 p. s. i. (pounds per square inch). Specimens ofthis composition gave improved results under the stress-rupture testsreferred to above and the composition proved to be extremely resistantto corrosion or oxidation at high temperatures.

Example VII This composition consists of titanium carbide (TiC),

a complex carbide solid solution containing columbium, tantalum,titanium and carbon and referred to herein as 4 Cb(TaTi)C, nickel andmolybdenum, in the following proportions, by weight:

Per cent TiC 55.0 Cb(TaTi)C 15.0 Ni 27.0 Mo 3.0

The hard composition of matter made from the mix above specified, by theprocedure hereinafter described, had a density of 6.30 grams per cubiccentimeter, a hardness of 87.0 on the Rockwell A scale, and a transverserupture strength at room temperature of 172,000 p. s. i. (pounds persquare inch). Specimens of this composition proved to be extremelyresistant to corrosion or oxidation at high temperatures.

Example VIII This composition consists of titanium carbide (TiC), acomplex carbide solid solution containing columbium, tantalum, titaniumand carbon and referred to herein as Cb(TaTi)C, nickel and molybdenum,in the following proportions, by weight:

Per cent TiC 55.0 Cb(TaTi)C 15.0 Ni 28.5 Mo 1.5

The hard composition of matter made from the mix above specified, by theprocedure hereinafter described, had a density of 6.22 grams per cubiccentimeter, a hardness of 86.3 on the Rockwell A scale, and a transverserupture strength at room temperature of 150,000 p. s. i. (pounds persquare inch). This composition proved to be extremely resistant tocorrosion or oxidation at high temperatures.

Example IX This composition consists of titanium carbide (TiC), acomplex carbide solid solution containing columbium, tantalum, titaniumand carbon and referred to herein as Cb(TaTi)C, nickel and molybdenum,in the following proportions, by weight:

Per cent TiC 56.0 Cb(TaTi)C 4.0 Ni 30.0 Mo 10.0

The hard composition of matter made from the mix above specified, by theprocedure hereinafter described, had a density of 6.24 grams per cubiccentimeter, a hardness of 87.5 on the Rockwell A scale, and a transverserupture strength at room temperature of 216,000 p. s. i. (pounds persquare inch). Specimens of this composition proved to be resistant tocorrosion or oxidation at high temperatures although not so resistant asthe compositions previously described.

Example X This composition consists of titanium carbide (TiC), a complexcarbide solid solution containing columbium, tantalum, titanium andcarbon and referred to herein as Cb(TaTi)C, nickel and molybdenum, inthe following proportions, by weight:

Per cent TiC 66.0 Cb (TaTi) C 4.0 Ni 28.5 Mo 1.5

The hard composition of matter made from the mix above specified, by theprocedure hereinafter described, had a density of 5.92 grams per cubiccentimeter, a hard- *5 ness of"85f.9 on the Rockwell Arscak, 'and 'atransverse rupture strength of 206,000 p. "s. 'i. '(pounds per squareim'rhi) The resistance to corrosion or oxidation at high temperatures ofthis "composition is good, although not quiteas good as that of thecompositions ofExampl'e's I to VIII, 'inclu'sive.

Example 5&1

This composition .consists o'fltitanium carbide I(TiC), aco'mplexcarbide .solid. solution containing cdlumbium, tantalum, titanium-andcaibon and referred to herein-as Cb(TaTi)C, nickel and molybdenum, inthe"'following proportions, by weight;

.Per cent The hard composition of matter made from the above specified,by the procedure .herein'a'fter described, hadadensityfof 5.82 gramspercubic centimeter, aihardness "of 87 .2 "on the Rockwell A scale, and "atransverse rupture strength at .room temperature .of *16'95500 p.1s. i.

(pounds per :square inch) The resistance .of specimens dftliiscomposition to corrosion or oxidation at hightem- "p'eratures was .foundto be good 'as compared with the compositions cfJExampIes I' to VII,inclusive, which were "classified as very, good,

:nxam 'le XII ilihis' composition consists of titanium :carbide (l-TiC),a complex carbide =solid isolut'ion containing Icolum'bium,

tautalum, titatitumrand carbonand :referredito herein as.bz(TaIii.)'C,.1nickel and "molybdenum, :in the '1 following:propottionsgbywweight:

' Per cent Fi'C ""6 60 Cb(T3Ti-)C c L 4:0

ferred to above. This composition proved to have a resis'tance -tocorrosion-or oxidation "at high temperatures *tnatwasclassified'as-good'as 'compared withthte resist- "fiance to corrosionand -oxidationo'f"'Examples I to 'VIII, in'clusivepwliich-was-characterized as very good.

Example XIII This composition consists of titanium carbide (TiC), acomplex carbide solid solution containing columbium, tantalum, titaniumand carbon and referred to herein as Cb (TaTi)C, nickel and molybdenum,in the following proportions, by weight:

Per cent TiC 42.0 Cb(TaTi)C 8.0 Ni 40.0 Mo 10.0

The hard composition of matter made from the mix above specified, by theprocedure hereinafter described, had a density of 6.80 grams per cubiccentimeter, a hardness of 83.6 on the Rockwell A scale, and a transverserupture strength at room temperature of 202,000 p. s. i. (pounds persquare inch). The resistance to corrosion or oxidation at hightemperatures of specimens of this composition, however, "werecharacterized good to poor.

Example XIV This composition consists of titanium carbide -(TiC), acomplex carbide solid solution containing columbium, tantalum, titaniumand carbon and referred-tobereinzas Cb(TaTi)C, nickel and molybdenum, inthe following proportions, by weight:

Percent TiC 52=0 Cb(TaTi)C -2 8.0 'Ni. .2510 .Mo -n. 4.510

The hard composition of matter made from the :mix above specified, bythe ,procedure hereinafter described, had a density of 6.56 -per cubiccentimeter, -a hardness of 89.6'on the :RockwellAscale,and-.aitransverse rupture strength at room temperature of .175 ,5.00,p.s. i. (pounds per square inch). However, the resistanceito @corrosion oroxidation at high temperatures of specimens ;of this composition was'found'to be zpoor.

The .compositions of matter above described may 'be made by the methodusually :used rfor making cemented car bide tool :compositionsiexceptthat certain refinements are desirable for producing the best :results.:carbide constituents of the composition, 'in Ithe form :of :crystalspassing through a sieve having .110!) -meshes rtO athe inch, and thepowdered *or rauxiliary :metal (nickel and molybdenum), having anaverage-.particlesize of about 25 microns,arezchargedtintoarsteel-ballmill. The halls used in the mill may beeithercementedcarbide (or :steel, since the presence of iron in these'zeoinpositions zis mot deleterious. The ball mill is then .filled with,a light petroleum solvent to exclude the air therefrom and is:thereupon sealed, and ,the'chargeis ball-milledifor from three to'six'days, tat the end of'which time the liquidin the mill and charge isremoved hy decantation andrevaporation and a temporary binder, sucl1=as0t25=to 11.00% of parafiin, is incorporated with the material. Theaverage Jparticle size of the material, ;at the end of ;the 'ballmilling operation, is from 1*to '5 microns. l the-(mixture is/nextpressed to theidesired shape, .or as near to -it as feasible. Althoughthis maybexdone by anyconventionalzpressing method, we have :foundtthatmuch more:de'sir-able results vare obtained by the useiof tthe-.-explosive pressing process, described [and claimed tin the spending:application for .United States-Letters 'Patent of Philip M. -McKenna,John =C. Redmond and Emlyn N. :Smith, Serial:No. 166,510,

filed August 6, 1947, entitled Explosive Pressing of RowtieredCompositions, rupon-rwhich U. .S. leettersrli'atent No. 2,648,125 were:granted 1onsAugust :11, 1953. .Accord- Sing -.to this :processZPI'ESSUI'CfiS applied rtouthe materialihydrostatically and rapidly fromall directions and very high pressures may be so applied. After pressingthe mixture to the desired form, the pieces may thereupon be sintered,or they may be further shaped by machining operations and, then,sintered. However, if any very complex shape is required, the materialin this form has insufiicient strength to withstand the necessarymachining operations and, in that case, it is given a preliminary heattreatment at temperatures of from 1900 to 2100 F. to give it sufficientstrength to withstand the pressure of machining or working with diamondtools, but such heat treatment is as may be required, by grinding with adiamond wheel.

The sintering temperatures used in producing the compositions ofExamples I to XIV, inclusive, are as shown by the following tabulation:

It is our belief that at the sintering temperatures employed the nickeland molybdenum alloy so that the metal binding the carbide particles ofthe composition together is an alloy of nickel and molybdenum. Theremaining metals of the iron group, that is, cobalt and iron, are

equivalents of nickel for use in the making of these hard compositionsof matter and cobalt or iron may be substituted for the nickel in theabove compositions.

To determine the resistance of the compositions to oxidation andcorrosion at high temperatures oxidation tests at 1800" F. were made onthe specimens in eleven eighteen-hour increments for a total time of 198hours. Those compositions which withstood the complete test of 198 hourswith no more than .003 inch of adherent oxide growth per face wereclassified as excellent. Such compositions usually oxidized in adecreasing parabolic rate indicative of self protection and long lifeunder severe oxidizing conditions. Those compositions which have thedecreasing parabolic rate type of oxidation resistance or a slow linearrate and in which an inherent oxide coating forms that is greater than.003 inch and less than .008 inch in 198 hours are classified as goodwith respect to resistance to oxidation or corrosion at hightemperatures. Those compositions which oxidize to a greater extent than.010 inch per face under the conditions specified above, or whichdevelop a loose, flaky or powdery coating but which do not lose shape in198 hours are classified as poor with respect to resistance to oxidationor corrosion at high temperatures.

From the foregoing examples it will be seen that compositions containingfrom 42 to 72% T iC, from 4 to 15% Cb(TaTi)C and from 20 to 50% of abinder metal alloy of nickel and molybdenum in which the molybdenumconstitutes from 5 to 25 of the alloy have very desirablecharacteristics. The most desirable characteristics appear to be thoseof compositions including from 55 to 72% Tic, from 8 to Cb(TaTi)C andfrom to 35% of a binder metal alloy of nickel and molybdenum in whichthe molybdenum constitutes from 5 to of the alloy.

We are aware that the compositions of matter herein described aresusceptible of considerable variation from the specific proportionsshown without departing from the spirit of our invention and, therefore,we claim our invention broadly as indicated by the appended claims.

Having thus described our invention, what we claim as new and useful,and desire to secure by United States Letters Patent, is:

1. A corrosion-resistant sintered hard composition of matter consistingof from 42% to 72% titanium carbide (TiC), substantially devoid of freetitanium, free carbon, oxides and nitrides, from 4% to 15% of a complexcarbide solid solution containing columbium, tantalum, titanium andcarbon, and from 20% to of a binder metal alloy of nickel andmolybdenum, in which the molybdenum constitutes from 5% to 25% of thealloy, said composition being characterized by a density of from 5.6 to6.8 grams per cubic centimeter, a hardness on the Rockwell A scaleexceeding 83.5, a transverse rupture strength, at room temperature,greater than 150,000 p. s. i. (pounds per square inch), and highresistance to oxidation at temperatures of 1800" F. and above.

2. A corrosion-resistant sintered hard composition of matter consistingof from to 72% titanium carbide (TiC), substantially devoid of freetitanium, free carbon, oxides and nitrides, from 8% to 15% of a complexcarbide solid solution containing columbium, tantalum, titanium andcarbon, and from 20% to 35% of a binder metal alloy of nickel andmolybdenum, in which the molybdenum constitutes from 5% to 25 of thealloy, said composition being characterized by a density of from 5.6 to6.3 grams per cubic centimeter, a hardness on the Rockwell A scaleexceeding 86, a transverse rupture strength, at room temperature,greater than 150,000 pounds per square inch, and high resistance tooxidation at temperatures of 1800" F. and above. I

3. A corrosion-resistant hard composition of matter consisting of about62% titanium carbide (TiC), substantially devoid of free titanium, freecarbon, oxides and nitrides, about 8% of a complex carbide solidsolution containing columbium, tantalum, titanium and carbon, and about30% of a binder metal alloy of nickel and molybdenum, in which themolybdenum constitutes about 15 of the alloy, characterized by a densityof about 6 grams per cubic centimeter, a hardness on the Rockwell Ascale of about 88.7, a transverse rupture strength at room temperature,of about 191,000 p. s. i., and high resistance to oxidation attemperatures of 1800 F. and above.

References Cited in the file ofthis patent UNITED STATES PATENTS2,023,413 Fetkenheuer Dec. 10, 1935 2,106,162 Balke Jan. 25, 19382,124,509 McKenna July 19, 1938 2,147,329 Willey Feb. 14, 1939

